This invention relates to a single image pickup tube type color television camera, and is more particularly concerned with an improved color television camera using an electrostatic focusing and electromagnetic deflection type image pickup tube.
In a compact color television camera using a single image pickup tube, color television signals are obtained by scanning an electron beam on the tube target including a plurality or optical stripe filters mounted thereon.
The optical filters have different stripe pitches from one another in order to generate different carrier frequencies during beam scanning corresponding to the respective pitches.
In a recently developed system of this type a 2/3 inch Vidicon tube is equipped with electrostatic focusing and electromagnetic deflection and achieves low power comsumption with compact size. In this newly developed compact image pickup tube, the cross section of the electron beam is much smallers than in the conventional electromagnetic focusing and deflection type image pickup tube. As a result, high accuracy of beam alignment is required to avoid the color shading defect in this color camera system. The advantages of reduced size and power consumption are only obtained with increased problems due to color shading. Color shading is the non-uniformity in color of the image which reduces the quality of the image.
In this type of color television camera system, signal modulation uniformity is a most important characteristic but is very difficult to obtain with each camera manufactured. In the manufacturing process, each camera will be structurally slightly different thereby effecting beam alignment, beam intensity and coma effect.
Thus in seeking to achieve a more compact and lower power consuming camera system, the following specific problems must be solved or eliminated to obviate the adverse effects of color shading. First, because of the smaller size of the tube, errors are introduced during scanning because of coma effects. Secondly, variations from tube to tube introduced during manufacture can result in misdirection of the electron beam within the tube. Finally, also because of imperfections introduced during manufacture, the energy density distrubution of the electron beam will vary from tube to tube. Each of these factors effects color shading because each causes non-uniform output signal modulation characteristics.
Electron beam alignment is usually achieved by using the weak magnetic field from the beam alignment coil or the like which is disposed on the tube in the vicinity of the beam control grid or Gl electrode gun of the pickup tube.
However, it is impossible to avoid such color shading defect completely only by adjusting the alignment coil or the like because is it very difficult to obtain the uniform signal output modulation from all over the beam scanning area due to coma error of the electron beam. There are also some inaccuracies of the electrodes because of assembling and winding distribution errors in the alignment coils and deflection coils.
Consequently, in the new 2/3 inch electrostatic focusing and electromagnetic deflection type tube, it becomes much harder to correct the color shading in each pickup tube than it was to correct for the conventional 1 inch electromagnetic focusing and deflection type tube.
It is therefore an object of this invention to provide an improved single pickup tube type color television camera system.
It is a further object of this invention to provide an improved single pickup tube type color television camera system using electrostatic focusing and electromagnetic deflection type tube.
It is a still further object of the invention to provide such an improved color television system which corrects for color shading.
These and other objects are accomplishedd in accordance with this invention by providing magnetic color shading correction means in the vicinity of the beam alignment means which is disposed near the beam control grid or Gl electrode of the electron gun means of the tube.